Hello @thesasuser,
to apply or install a new maintenance is nothing more than a simple upgrade-in-place. Generally speaking, it should be quite straight forward: to update binaries (with SAS Deployment Wizard), and update the configuration (with SAS Deployment Manager, normally triggered automatically by the SDW), so 2 steps. However, the Guide to Updates can help much better with this question, specially since some products and some maintenances might contain specifics.
Regarding your very last question: maintenaces are like mega-containers of the hotfixes released for the previous mantenances and, generally speaking, some new features.
Sometimes, it might even contain new applications, but those new applications would require to update your deployment plan file (plan.xml) with the new components and, after upgrading in place and updating your plan file, you can deploy them with SAS deployment wizard.
Hope it helps,
Kind regards,
Juan